When do you need to use a trench box

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# CONSTRUCTION STANDARD (cont.) ## R 408.[redacted postal code]. Benching and sloping. - Rule 944. (1) The angle of repose shall be flattened when an excavation has water conditions, silty materials, loose boulders, or areas where erosion, deep frost action, or slide planes appear. (2) When benching the side of an excavation, the vertical rise shall not be more than 5 feet and the step back shall extend at least to the angle of repose as required by table 1. (3) When benching a side of a trench, the height of the lower bench shall not be more than the lesser of 5 feet or width of the trench measured at the bottom. (4) An employee shall not be permitted to work on sloped or benched excavations at levels above another employee, except when an employee at the lower level is protected from the hazard of falling, rolling, or sliding material or equipment. ## R 408.[redacted postal code]. Trenching boxes and shields. - Rule 945. (1) Portable trench boxes or sliding trench shields may be used for theprotection of personnel in place of a shoring system or sloping. Where such trench boxes or shields are used, they shall be designed, constructed, and maintained in a manner that provides protection equal to or greater than the sheeting or shoring required for the trench. (2) The use of benching in conjunction with a portable trench box is permitted when the toe of the trench box is not more than 2 feet above the trench bottom, but only if the trench box is designed to resist the forces calculated for the full depth of the trench and if there are no indications, while the trench is open, of a possible cave-in below the bottom of the trench box. (3) An employee shall not be allowed in shields when shields are being installed, removed, or moved vertically. (4) Shield systems shall not be subjected to loads exceeding those which the system was designed to withstand. (5) Shields shall be installed in a manner to restrict lateral or other hazardous movement of the shield …

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# Trenching and Excavation (cont.) ## Temporary protective structure (cont.) - Trench Boxes are commonly used in open areas that are away from utilities, roadways, and foundations. Trench boxes can be used to protect workers in cases of cave-ins, but not to shore up or support trench walls. They can support trench walls if the space between the box and the trench wall is backfilled with soil and compacted properly. Otherwise, a cave-in or collapse may cause the trench box to tilt or turn over. Workers should not be present in the box when it has to be moved. - Other: In some cases, the trench or excavation walls are made of rock but are not entirely stable. Support the walls by using rock bolts, wire mesh, or a method that provides equivalent support. ## What should NOT be done during an excavation? - Do not enter an unprotected trench deeper than 1.2 metres (4 feet), or as specified in the legislation. - Do not start digging before locating and de-energizing the buried services. - Do not enter a trench before testing the air for hazardous gasses and vapours, or the lack of oxygen. - Do not place the sections of pipes, piles of spoil, unused tools, and timber, and other materials within 1 metre from the trench's edge. - Do not rely on natural freezing to act as a method of soil stabilization. - Do not work under suspended or raised loads and materials. - Do not stand behind a backing vehicle. ## What can be included in a trenching and excavation inspection checklist? The following are some points to consider. Each circumstance will be different, so be sure to adapt the questions to suit your situation. ## Underground or Utility Services - Know the contact numbers? - Located, identified and informed respective parties? - Grounded, isolated, de-energized, or protected from unplanned release? ## Housekeeping Trenching and Excavation CCOHS

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# Temporary Protective Structures (cont.) (5) If a worker is in a trench that is more than 1.2 m deep, an employer shall ensure that a competent worker is stationed on the surface to (a) alert the worker in the trench about the development of hazards; and (b) provide assistance in an emergency. (6) If a worker is required or permitted to enter a trench, an employer shall (a) install ladders, stairways or ramps to provide a safe means of entrance to and exit from the trench; and (b) ensure that the ladder, stairway or ramp is located not more than 8 m from a worker working in the trench. (7) An employer shall ensure that a worker who could be required or permitted to enter a trench is instructed in and complies with the requirements of this section. - Excavated Shafts and Tunnels 271. (1) An employer shall ensure that (a) during excavating, the walls of an excavated shaft or tunnel are retained by temporary protective structures that are adequate (i) for the type of soil, and (ii) to prevent collapse or cave-in of the walls of the excavated shaft or tunnel; (b) during the excavating of an excavated shaft that is 3 m or more deep or of a tunnel, the walls of the shaft or tunnel are retained by temporary protective structures designed and certified by a professional engineer and constructed, installed, used, maintained and dismantled in accordance with that design; (c) a solid or wire mesh fence not less than 1 m high, or other equally effective means of preventing material from falling into an excavated shaft or the surface opening of a tunnel, is provided around that shaft or opening; and (d) substantial gates that are not less than 2 m high are installed in each opening in a fence provided under paragraph (c) and the gates are kept closed other than when in use. (2) A worker who opens a gate referred to in paragraph (1)(d) shall close the gate after the worker no longer has a need to keep the gate open. (3) An employer sh…